The present invention relates to archery products, and more particularly to a riser and a cam system that maintain alignment and provide consistent, proper nock travel.
Conventional compound and crossbow archery bows include a bowstring and a set of power cables that transfer energy from the limbs and cams, eccentrics or pulleys (which are all referred to generally as “cams” herein) of the bow to the bowstring, and thus to an arrow shot from the bow. The cables and bowstring are strung from a cam on one limb to a cam on another limb. The power cables are guided by a cable guard in a lateral position relative to the bowstring so as to not interfere with movement of the bowstring or the travel of an arrow on the bowstring. The function of the cams is to provide a mechanical advantage so that energy imparted to the arrow is a multiple of that required of an archer to draw the bow.
Generally, there are single cam systems and dual cam systems, with various configurations of each. A single cam system usually includes a single cam mounted on one limb and a single track pulley mounted on the other limb of the bow. One dual cam system includes two cams, each mounted on opposing limbs of a bow. Two cables and a single bowstring are strung between both cams; however, one end of each cable is yoked to an axle upon which a cam rotates. Another variant of the dual cam system, often referred to as a binary cam system, has opposing power cables strung about both cams in respective take-up and payout tracks, and a bowstring strung in respective bowstring tracks in both cams. The upper and lower cams in this system usually are mirrored and identical in size and shape, so that the cams self-correct for timing and synchronization, and automatically equalize for imbalances in the bow.
Regardless of the type of cam system, they all work somewhat similarly. For example, when an archer draws the bow from an undrawn state to a drawn state, the bowstring rotates the cams rearward, and the force and energy applied by the archer to draw the bow is transferred to the limbs, typically bending the limbs so that they effectively store energy in their bent or flexed configuration. When the archer releases the bowstring, the energy stored in the limbs assists in rotating the cams and propelling the bowstring to its original position in an undrawn state.
In many conventional cam systems, as mentioned above, the power cables are held by a cable guard, laterally outward from the centerline of the bow and bowstring (when viewed from the rear of the bow), so as to keep the power cable out of the way of the bowstring and any nocked arrow. With the cables so laterally maintained, they exert a lateral force on the upper and lower cams. In turn, this pulls the tips of the respective limbs laterally as well, toward whatever side of the bow the cable guard is on. As a result, the limbs exert a moment on the riser where the limbs connect to the riser. If too much moment is applied, the riser twists slightly, which causes the upper and lower cams to move laterally out of alignment with one another and a centerline of the riser. This is unfavorable, as it throws off the alignment of those cams and their subsequent proper function. Generally, the lower portion of the riser has historically shown more twisting than the top.
Manufacturers have attempted to address this twisting of the riser near the limbs, and in particular, in the lower riser portion, by simply increasing the rigidity of the riser in the lower half of the riser so it will not twist as much. This typically is done by adding more material, such as more aluminum structure, in the lower half of the rise. What this does, however, is add weight and bulk to the bow, throws off its center of gravity, and does not adequately address the alignment of the upper and lower cams.
Further, most conventional compound bows are designed to have the arrow located at the geometric center of the riser and bowstring, which in turn promotes even vertical nock travel of the arrow. In turn, such bows are structured so that the grip of the riser, where the archer holds the bow, is located a large distance below the geometric center of the riser. As a result, such bows are top heavy, so they tend to tilt forward and feel unbalanced to some archers. This can in some cases affect arrow travel and overall accuracy of the bow.